1. The Field of the Invention
This invention relates to tube couplings for connecting a pair of conduits through which a cable extends and more particularly although not exclusively for connecting a pair of conduits through which an optical fiber cable extends.
2. The Relevant Technology
Optical fibers are now commonly used for voice and data transmission lines. Optical fiber bundles are usually laid in conduiting to protect the fibers whether passing through underground channels or within buildings. Lengths of plastic conduit are provided coupled together by push-in tube coupling. The fiber is delivered through the conduiting by high pressure air which acts on a roughened surface of the fiber and draws the fibers through the conduiting. Once the fiber has been laid in the conduiting, it is desirable to be able to create a seal between the coupling and fiber to prevent passage of gas along the conduiting. Gas can enter the conduiting from a leak in the ground outside a building and if it is allowed to enter the conduiting and travel into the building to which the conduiting leads, there is a risk of a gas build up and possible explosion. There is therefore a need to isolate the interior of the conduit leading into the building from the rest of the conduit.
EP-A-0363188 discloses a tube coupling for connecting conduiting in which an optical fiber is laid. The coupling includes a complex form seal located in the coupling having end portions to receive and seal with conduit ends inserted into the coupling and a central section which can be displaced as air pressure to allow passage of an optical fiber through the coupling and which springs back to engage the tube once the air pressure is released. With this arrangement it is difficult to ensure an effective reliable seal with the fibre.